In conventional OFDM communication, a transmitting-side apparatus transmits a burst unit signal such as that shown in FIG. 1, for example, to a predetermined receiving-side apparatus, as adopted in IEEE 802.11 and the like, for example. As shown in FIG. 1, a burst unit signal includes guard intervals (GI), a preamble for transmission path estimation, and an information signal (data). In a burst unit signal, the transmission path estimation preamble undergoes IFFT (inverse fast Fourier transform) processing, and the information signal undergoes predetermined modulation processing and IFFT processing.
The receiving-side apparatus detects the FFT (fast Fourier transform) processing start timing by calculating a correlation value between the IFFT-processed transmission path estimation preamble and the transmission path estimation preamble in the received burst unit signal (received signal). The receiving-side apparatus then extracts the transmission path estimation preamble and information signal from the received signal by performing FFT processing on the received signal in accordance with the detected start timing. The receiving-side apparatus also performs transmission path estimation using the extracted transmission path estimation preamble, and performs information signal demodulation using the result of transmission path estimation. By this means, the receiving-side apparatus can extract a demodulated signal.
However, there is the following problem in conventional OFDM communication as described above. Namely, in conventional OFDM communication as described above, the number of symbols in a transmission path estimation preamble in a burst unit signal is fixed (in FIG. 1, one symbol).
In general, when a transmission path estimation preamble with a larger number of symbols is used on a fixed basis as a transmission path estimation preamble, the error rate characteristics of a demodulated signal obtained by the receiving-side apparatus are good. However, as a transmission path estimation preamble is not an information signal, using a transmission path estimation preamble with a larger number of symbols is equivalent to increasing the proportion of a burst unit signal occupied by superfluous information. That is to say, when a transmission path estimation preamble with a larger number of symbols is used, information signal transmission efficiency falls.
On the other hand, when a transmission path estimation preamble with a smaller number of symbols is used on a fixed basis as a transmission path estimation preamble, the proportion of a burst unit signal occupied by superfluous information is reduced, and information signal transmission efficiency is consequently improved. However, depending on conditions such as channel quality, there is a high possibility of deterioration of the error rate characteristics of a demodulated signal obtained by the receiving-side apparatus.
Thus, in above-described conventional OFDM communications, there is a problem in that it is difficult to achieve both an improvement in demodulated signal error rate characteristics and an improvement in information signal transmission efficiency.